structure IntExtra = struct
    fun expt (0, _) = 0
      | expt (1, _) = 1
      | expt (base, 0) = 1
      | expt (base, 1) = base
      | expt (base, exponent) =
        base * expt (base, exponent - 1);
    fun even num = (num mod 2) = 0;
    fun odd num = (num mod 2) = 1;
end;
